Inhibiting corrosion of copper with tetrazoles



United States ABSTRACT OF THE DISCLOSURE Certain tetrazoles are shown to be effective for inhibiting the corrosion of copper containing metals in contact with corrosive aqueous liquids.

This invention relates to a process for inhibiting corrosion of copper-containing metal surfaces. More particularly( the invention relates to a process whereby corrosion of copper metal caused by contact with a corrosive aqueous media is inhibited by means of the compounds ofthis invention. f

Corrosion of copper-containing metal surfaces is a paramount problem in a wide variety of industrial and consumer water systems. Copper and its alloys are often employed in cooling towers, radiators for automobiles, home and industrial-air conditioning and heating plants, as well as in a wide variety of recirculation and water transfer units. Constant attention is required in many of these systems to prevent or control excessive corrosion of the. copper and copper alloy surfaces.

Even more severe is the problem of corrosion of copper and copper alloys in contact with aqueous systems which contain an appreciable amount of divalent sulfur-containing compounds. Contamination of the aqueous media by hydrogen sulfide and various other compounds which contain an active divalent sulfur group is common in many industrial operations such as refineries, steel mills, and other plants where sulfur-containing organic chemicals are manufactured, processed or consumed. Also, not a small portion of the natural waters of the United States contain at least a minor amount of dissolved divalent sulfur compounds. The presence of these materials has been found to accelerate the corrosive attack of aqueous media on copper and copper alloys.

Many attempts have been proposed to control the copper and copper alloys corrosion. A number of effective materials have been developed which are capable of reducing significantly the amount and rate of corrosion. One particular compound which is used extensively to prevent .corrosion of copper-containing metals is mercaptobenzothiazole. However, this material, as well as most of-the other copper corrosion inhibitors available today, is-substantially less effective in the presence of hydrogen sulfide and other divalent sulfur-containing compounds. Sometimes, in fact, the addition of a normally effective copper corrosion inhibitor to a system which contains an appreciable amount of a divalent sulfur compound actually causes more severe corrosion than would have occurred without benefit of the inhibitor.

Accordingly, it is a specific object of this invention to atent provide a satisfactory process for inhibiting the corrosion of copper-containing metals by aqueous media.

Another object of this invention is to provide a process which is effective even in the presence of divalent sulfurcontaining compounds.

A further object of this invention is to provide a class of compounds which are capable of achieving substantially complete corrosion inhibition under most normally encountered conditions.

Other objects will appear hereinafter.

In accordance with the invention, it has now been discovered that the objects of this invention may be accomplished by the process of this invention. Specifically, the process comprises adding a corrosion inhibiting amount of a tetrazole defined hereinafter to an aqueous media which normally is corrosive to copper-containing metal surfaces, thereby substantially inhibiting the amount and rate of corrosion of said metal. Also, it has been discovered that the compounds of this invention are effective when used in the presence of active sulfur-containing compounds dissolved in the aqueous media.

The compounds which have been found to be surprisingly effective in the process of this invention may be defined by the following formula:

N N i All.

Nr J.1-...-. Na where n is an integer from 0 to 1, and D represents a divalent organic radical containing less than 25 carbon atoms, said radical being composed of elements selected from the group consisting of C, H, O, N and S. A preferred class of radicals are those radicals having up to 10 carbon atoms.

The preparation of the tetrazoles having the above formula may generally be accomplished by the reaction of a nitrile group with hydrazoic acid or the weak base salts of hydrazoic acid such as ammonium azide. This reaction can be carried out in a solvent system which will vary depending upon the particular nitrile being employed. For example, nitriles of the formula R-OCEN may be reacted at room temperature in the presence of ether to yield the corresponding tetrazole. When the nitrile has the formula R-SCEN, synthesis of the tetrazole is effectively carried out in solvents such as ethylene glycol dimethyl ether at elevated temperatures such as around C. When the nitrile is of the type having the formula RCEN, even more severe conditions are necessary to form the corresponding tetrazole, and in this instance, effective reaction conditions are those using dimethyl formamide at a temperature of approximately 96 to 100 C. Preparation of tetrazoles is a known art, and the various embodiments of the particular synthesis may be left to the manufacturer.

Specific examples of the compounds of this invention where n equals 1 are the various 5,5'substituted bis tetrazoles such as 5,5'methylene bis tetrazole and 5,5'tetramethylene bis tetrazole. A wide variety of these bis tetrazoles may be prepared, with the only limitation being the difficulty in obtaining the di-nitrile starting reactant. It is greatly preferred to employ tetrazoles of this class where D represents an alkylene radical of from 1 to 5 carbon II II o N As stated above, the process of this invention comprises adding a corrosion inhibiting amount of a tetrazole as defined above to an aqueous media which is normally corrosive to copper-containing metal surfaces, thereby inhibiting corrosion of said surfaces. The amount of the tetrazole which may be added to effectively inhibit corrosion will vary depending upon a number of factors, such as temperature, pH, and the like. Normally, from 1 p.p.m. to 50 p.p.m. of the tetrazole will satisfactorily inhibit corrosion.

A particularly preferred embodiment of this invention is to employ the tetrazoles defined above in aqueous systems which contain an amount of divalent sulfur-containing compounds dissolved therein. It has been found that the corrosion inhibiting properties of the above tetrazoles are surprisingly effective, and sometimes even improved, when such compounds are present. The tetrazoles of this invention may effectively be used in systems which contain divalent sulfur compounds, and, when particularly severe coppers and copper alloy corrosion exists, the effectiveness of the tetrazoles may even be increased by the intentional addition of compounds which contain these normally corrosive active rsulfur groups. The most common example of this class of compounds is hydrogen sulfide. Examples of other compounds falling within this class are: carbon disulfide, thionophosphoric acid and salts thereof, thiosulfates, xanthates, tetrathianates, organic polysulfides such as dimethyl polysulfide, alkali metal and ammonium sulfides, polyamine-sulfur complexes, trithiocarbonates such as alkyl trithio ortho formatc, mercaptals which are reaction products of aldehydes and mercaptans, mercaptols which are reaction products of ketones and mercaptans, thioketones, thioaldehydes and the like. Generally, it is believed that compounds such as those exemplified above release an active sulfur group which promotes corrosion of aqueous media in contact with copper and copper-containing metals. The tetrazoles of this invention have been found to be effective in inhibiting the corrosive effect of the active sulfur groups.

The following examples are presented to illustrate the various embodiments of this invention. These examples are merely intended to be illustrative and are not to be construed as limiting upon the appended claims.

EXAMPLES A number of the tertazoles of this invention were prepared and evaluated as corrosion inhibitors for copper and copper alloys. The test method employed here consisted of a system whereby the aqueous media was recirculated by means of pumps to allow the media to continually pass in contact with a copper-containing metal surface. The temperature of the recirculated system was maintained by means of an electrically controlled oil bath. After a predetermined number of hours, the coppercontaining metal surfaces were then withdrawn and examined to measure the amount of corrosion. Results of these tests are reported in percentage protection, based on the corrosion of a blank run wherein no corrosion inhibitor was employed.

In Table I below, the results of corrosion inhibiting tests of a number of tetrazoles of this invention are presented. For simplification purposes, only the variables n and D of the general formula, as defined hereinabove, are presented. As can be readily determined, a wide variety of tetrazoles falling within the general formula are capable of providing excellent corrosion inhibition.

A number of other tetrazoles which are effective inhibitors of copper corrosion and have the general formula of the compounds of this invention may be prepared from available nitriles and di-nitriles which will yield tertazoles where D will be a divalent organic radical of less than 25 carbon atoms, said radical being composed of the elements carbon, hydrogen, oxygen, nitrogen and sulfur.

Further experiments were performed using a similar test apparatus to demonstrate the surprising effectiveness of the compounds of this invention when used in aqueous media which contain an active divalent sulfur-containing compound dissolved therein. Also, to demonstrate the expected adverse effect of these mercapto radicalsupon conventional copper corrosion inhibitors, tests were made to similarly evaluate mercaptobenzothiazole. Presented below in Table II are the results of these tests. In Runs A and B, mercaptobenzothiazole was used to show the substantial lessening of the corrosion inhibiting properties of this corrosion inhibitor when used in the presence of hydrogen sulfide. Runs C and D were made using tetrazole No. 1 of Table '1. Similarly, tetrazole No. 6 was employed in Runs E and F, while tetrazole No. 8 was employed in Runs G and H, as shown in Table H. It is clearly evident from the data presented in Table II that the compounds of this invention are surprisingly effective in inhibiting corrosion of copper-containing metal surfaces which are contacted with aqueous media having an amount of active sulfur-containing compounds dissolved therein.

P.p.m. Percent Sull Protection, (As HES) At 10 p.p.m.

Run No. Corrosion Inhibitor orcenoenomc While the compounds of this invention have been shown to be effective in the process of this invention it is not contemplated that the invention be limited solely to their use as the sole corrosion inhibitor employed. It is oftentimes the normal practice in the corrosion inhibiting art to include other materials in a formulation for the prevention of corrosion of other metals present in order to simplify treatment steps. It has been found that the process of this invention is not materially aflz'ected by the presence of other corrosion inhibiting compounds. Accordingly, the normal practice of multiple additive formulation may be practiced without departing from the spirit of this invention.

Having thus described the invention, what is claimed is:

1. An aqueous fluid which is non-corrosive to copper containing metal surfaces which comprises a major portion of an aqueous liquid which is normally corrosive towards copper metal surfaces and from 1 to 50 ppm. of a tetrazole having the formula:

and

6 2. The aqueous fluid of claim 1 wherein said fluid also contains a compound having a divalent sulfur group. 3. The aqueous fluid of claim 2 where said compound is hydrogen sulfide.

References Cited UNITED STATES PATENTS 2,941,953 6/1960 Hatch 212.7 X 3,295,917 1/1967 Cotton 21-2.7 X

OTHER REFERENCES Chemical Abstracts, 1961, vol. 55, p. 781911).

LEON 'D. ROSDOL, Primary Examiner.

I. GLUCK, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,408,307 October 29, 1968 Edwin S. Troscinski et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 62, "tertazoles" should read tetrazoles Column 4, TABLE I third column, line 4 thereof, "m-HO C H should read mNO C H same table, third column, lines 5 to 7, "C should read -CH same column 4, line 25, "tertazoles" should read tetrazoles line 58, "Tatrazole" should read Tetrazole Column 5, line 15,

"m-NO C I-I should read mNO (lJ H Signed and sealed this 21st day of April 1970.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents 

